1. Field of the Invention
The present invention generally relates to multi-layered golf balls and more particularly to golf balls having at least one layer made of polyester/plasticizer compositions. The golf ball includes a core having at least one layer and a cover having at least one layer. The polyester/plasticizer composition may be used to form any core, cover, or other layer in the golf ball. In one version, the composition comprises a blend of polyester, plasticizer, and polyamide. Preferably, a polyester-ether copolymer is used in the composition.
2. Brief Review of the Related Art
Multi-layered, solid golf balls are used today by recreational and professional golfers. Basically, these golf balls contain an inner core protected by a cover. The core acts as the primary engine for the ball and the cover helps provide the ball with durability and wear-resistance. The core and cover may be single or multi-layered. For example, three-piece golf balls having an inner core, inner cover layer, and outer cover layer are popular. In other instances, golfers will use a four-piece ball containing a dual-core (inner core and surrounding outer-core layer) and dual-cover (inner cover layer and surrounding outer cover layer). Intermediate layer(s) may be disposed between the core and cover layers to impart various properties. Thus, five-piece and even six-piece balls can be made. Normally, the core layers are made of a natural or synthetic rubber material or highly neutralized ionomer polymers (HNPs). These ionomer polymers are typically copolymers of ethylene and methacrylic acid or acrylic acid that are partially or fully neutralized. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer.
Such ethylene acid copolymer ionomer resins are relatively hard materials having good durability, cut-resistance, and toughness. The ionomers may be used to make cover, intermediate, and core layers. When used as a core material, the hard ionomer resin helps impart a higher initial velocity to the golf ball. This is particularly advantageous for driver shots off the tee. The ball tends to have good flight distance. However, one disadvantageous feature of such balls is they tend to have a hard “feel.” Some players experience a harsher, less comfortable feel when their club face makes contact with these hard balls. The player senses less control and the harder ball tends to have low initial spin. It is generally more difficult to hit hard balls with the proper touch and control. This can be particularly troublesome when making approach shots with irons near the green.
Thus, the industry has looked at numerous non-ionomeric materials such as polyolefins, polyamides, polyesters, polyurethanes, polyureas, fluoropolymers, polyvinyl chlorides, polycarbonates, polyethers, polyimides, and the like for making various components and layers in golf balls. For example, Nakamura et al, US Patent Application Publication 2002/0037778 discloses golf balls having a multi-layered core construction including a center core and outer core layer; and a cover. The center core is made of a thermoplastic resin or elastomer, and examples of these materials include ionomer resins, thermoplastic polyamide elastomers, and thermoplastic polyester elastomers. The outer core is preferably made of a rubber composition. The center core has a Shore D hardness of 15 to 50, and the outer core layer has a Shore D hardness near the interface of the center core which is 1 to 15 units higher than the Shore D hardness of the center core.
Nakamura et al, US Patent Application Publication 2002/0039933 also discloses golf balls having a multi-layered core construction including a center core and outer core layer. The center core is made of thermoplastic resins or thermoplastic elastomers, such as nylons, polyarylates, ionomer resins, polypropylene resins, thermoplastic polyurethane elastomers and thermoplastic polyester elastomers In the '778 Publication, the outer core layer has a two-layer construction in which the resin or resin/rubber mixture is used to form the inside layer and a rubber composition is used to form the outside layer; and a cover.
In Loper et al., US Patent Application Publication 2006/0172823, four-piece golf balls having one or more core layers, an inner mantle layer, an outer mantle layer, and one or more cover layers are disclosed. In one embodiment, the composition of inner mantle layer and/or the outer mantle layer comprises a blend of polyamide or copolymeric polyamide and another polymer. According to the '823 Publication, suitable other polymers for the blend include ionomers, co-polyetheramide elastomers, polyarylates, polyolefins, polyoctenamers, polyurethanes, styrenic block copolymers, metallocene catalized polymers, and polyesters.
Although some non-ionomeric compositions containing polyesters as mentioned above may be somewhat effective for making certain components and layers in a golf ball, there is still a need for new compositions that can impart high quality performance properties to the ball. Particularly, there is a continuing need for improved core constructions in golf balls. The core material should have good toughness and provide the ball with high resiliency. The core material, however, should not be excessively hard and stiff so that properties such as feel, softness, and spin control are sacrificed. The present invention provides golf balls having an optimum combination of properties.